Sayu Shirotsume is the main protagonist of the visual novel series 'Shirotsume Souwa.' She is a high school girl who becomes entangled in mysterious and supernatural events after moving to a quiet, rural town. Sayu is known for her kind-hearted and determined personality. Throughout the story, she struggles to uncover secrets about her family's past and the enigmatic occurrences surrounding her new home, driving the plot forward and connecting deeply with other characters in the series.